When a spark plug is initially being installed in an internal combustion engine, it is usually necessary to set the gap between electrodes and it is always desirable to check the setting. The same is true when a plug is being removed, cleaned or checked, and replaced.
Normally, two tools are required for these tasks, apart from any devices for cleaning the spark plug. One tool is a wrench for removing the plug and for reinstalling it, commonly a socket type of wrench of a size suitable to a class of spark plugs, and the other tool is a gauge, or set of gauges, for establishing the proper gap setting, depending upon the nature of the engine and its intended operating condition, and on the type of plug.
It has been recognized that considerable convenience would result from the development of a tool having the socket wrench and gauge combined, but the efforts in that direction have not been fully satisfactory. Examples of the prior art are found in the following patents.
U.S. Pat. Nos. 2,184,340; D. E. Ferlin PA1 2,313,174; F. C. Shock PA1 2,564,812; C. McGuire PA1 2,578,975; J. H. Horne PA1 2,693,124; L. J. Rozankowski PA1 2,869,160; C. E. Murcott PA1 3,680,159; Wharram.
In most of these references the tools and gauges are designed for use with articles other than spark plugs and the wrenches shown are simply not suitable for installing or removing plugs. In Wharram, the wrench of which is designed for use with spark plugs, a thickness gauge of a single thickness dimension is attached to or formed as a part of, a handle attached to a socket. Not only is this gauge capable of only measuring one thickness or gap width, but the manner of attaching the gauge to the handle has several disadvantages including the fact that the gauge and handle must be removed from the socket so that the socket can be used in some of the more modern automobile engines in which lateral access to a plug is often limited. This means that the gauge can easily be misplaced.